Reasons for the low accumulation level of aphid transmission factor protein in infected leaves with an aphid-non-transmissible cauliflower mosaic virus isolate, CM1841.

The synthesis and accumulation of aphid transmission factor protein (p18) in cauliflower mosaic virus (CaMV)-infected turnip protoplasts were examined in time course and pulse-labelling experiments, comparing an aphid-non-transmissible isolate (CM1841) with an in vitro recombinant aphid-transmissible CaMV (CMBX) generated from the CM1841 isolate. There was little difference in the synthesis and accumulation of p18 between CM1841- and CMBX-infected protoplasts. When the accumulation of p18 in infected leaves was monitored from 3 to 28 days post-symptom emergence (p.e.) by Western blotting, the amount of p18 accumulated in CM1841-infected leaves continuously decreased from 3 days p.e. throughout the experimental period, whereas the amount of p18 in CMBX-infected leaves was lowest at 3 days p.e. and increased thereafter. These results suggested that CM1841 differed from CMBX not in the synthesis of p18 but in the stability of p18 in infected leaves.